With harvesting machines, a measurement of crop throughput is sensible for the purpose of an automatic adjustment of crop conveyors and or crop processing devices. The crop throughput is also frequently measured for the purpose of the management of partial areas. Furthermore, with the aid of the measured crop throughput, the advance speed of the harvesting machine on a field can be adjusted by a corresponding control in such a we that a desired crop throughput is attained, which, for example, corresponds to an optimal utilization of the harvesting machine. It is normal to determine crop throughput with corresponding sensors in the harvesting machine. Since the measurement is carried out only after the crops were gathered by the harvesting machine, a sudden change of the crop throughput with such sensors can no longer be compensated for by a corresponding adaptation of the traveling speed, which can result in a reduced or excess loading of the crop processing devices or even in the processing devices becoming plugged.
DE 10 2008 043 716 A1 describes a harvesting machine equipped with a device to record the number of plants on a field, the device including a transmitter, which radiates electronic waves in the visible or near-infrared range from the machine at a forward and downward inclination onto plants that are in front of the machine, and a receiver, which works with a local or angular resolution and which receives waves reflected by the plants in the plant group and/or by the earth. An evaluation device determines the transit time of the waves of the transmitter to the recipient at various points along a measurement direction running transverse to the forward direction of travel and determines the number of plants with the aid of the variation of the recorded transit times. A recording of the plant density is based on the fact that with dense groups of plants, almost all waves are reflected by the foliage of the crops or plants, which means a rather low variation of the recorded transit times, whereas with thin plant densities, a greater fraction of the waves is reflected by the earth, which, at the pertinent sites, results in substantially longer transit times of the light and greater variations of the transit times along the measurement direction. The density of the plant group is determined with the aid of statistical parameters (that is, the variations in the transit times of the waves), using a calibration table established by experiments and permanently stored, determined and multiplied with the vertical area of the plants, so as to ascertain the number of plants to be expected during harvesting. Taking into consideration the cutting height and the type of plant, a calibration of the detected number of plants follows with the aid of the measurement values of a crop throughout sensor of the harvesting machine, wherein for the adjustment of the calibration data, one has recourse to an expert system or a neuronal network, and the calibration data can again be determined from time to time, so as to take into account changed ambient conditions. Here, the connection between the statistical parameters and the density of the plants is accordingly determined by experiments and permanently pre-specified, so that it does not lead to optimal results under all operational conditions.